Blender UI simplification, template_header_3D, mesh selection mode
Here is the solution:

if obj and obj.mode == 'EDIT':
    row = layout.row(align=True)
    row.prop(toolsettings, "mesh_select_mode", icon='VERTEXSEL', text='', index=0, toggle=True)
    row.prop(toolsettings, "mesh_select_mode", icon='EDGESEL', text='', index=1, toggle=True)
    row.prop(toolsettings, "mesh_select_mode", icon='FACESEL', text='', index=2, toggle=True)


Using the index parameter it is possible to select elements of the bool vector.